Ligand-Shell Engineering of a Au28 Nanocluster Boosts Electrocatalytic CO2 Reduction

Linkage Engineering in Covalent Organic Frameworks for Metal-Free Electrocatalytic C2H4 Production from CO2

Electrocatalytic carbon dioxide reduction reaction (CO2RR) to produce ethylene (C2H4) is conducive to sustainable development of energy and environment. At present, most electrocatalysts for C2H4 production are limited to the heavy metal copper, meanwhile, achieving metal-free catalysis remains a challenge. Noted piperazine with sp3 N hybridization is beneficial to CO2 capture, but CO2RR performance and mechanism have been lacking. Herein, based on linkage engineering, we construct a novel high-density sp3 N catalytic array via introducing piperazine into the crystalline and microporous aminal-linked covalent organic frameworks (COFs). Thanks to its high sp3 N density, strong CO2 capture capacity and great hydrophilicity, aminal-linked COF successfully achieves the conversion of CO2 to C2H4 with a Faraday efficiency up to 19.1 %, which is stand out in all reported metal-free COF electrocatalysts. In addition, a series of imine-linked COFs are synthesized and combined with DFT calculations to demonstrate the critical role of sp3 N in enhancing the kinetics of CO2RR. Therefore, this work reveals the extraordinary potential of linkage engineering in COFs to break through some catalytic bottlenecks.

Assembly of Copper Alkynyl Clusters into Dimensionally Diverse Coordinated Polymers Mediated by Pyridine Ligands

Surface ligands play crucial roles in modifying the properties of metal nanoclusters and stabilizing atomically precise structures, and also serve as vital linkers for constructing cluster-based coordination polymers. In this study, we present the results of the solvothermal synthesis of eight novel copper alkynyl clusters incorporating pyridine ligands using a one-pot method. The resulting compounds underwent characterization through elemental analysis, Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD). Our observations revealed that distinct pyridine ligands with varying lengths and coordination sites exert significant influence on the structure and dimensionality of the clusters. The structural diversity of these clusters led to the formation of one-dimensional (1D), two-dimensional (2D), or dimer arrangements linked by seven pyridine bridging ligands. Remarkably, these complexes exhibited unique UV-vis absorption and photoluminescence properties, which were influenced by the specific bridging ligand and structural framework. Furthermore, density functional theory (DFT) calculations demonstrated the capability of the conjugated system in the pyridine ligand to impact the band gap of clusters. This study not only unveils the inherent structural diversity in coordination polymers based on copper alkynyl clusters but also offers valuable insights into harnessing ligand engineering for structural and property modulation.

Enzyme-activatable charge transfer in gold nanoclusters

Surface-protecting ligands, as a major component of metal nanoclusters (MNCs), can dominate molecular characteristics, performance behaviors, and biological properties of MNCs, which brings diversity and flexibility to the nanoclusters and largely promotes their applications in optics, electricity, magnetism, catalysis, biology, and other fields. We report herein the design of a new kind of water-soluble luminescent gold nanoclusters (AuNCs) for enzyme-activatable charge transfer (CT) based on the ligand engineering of AuNCs with 6-mercaptopurine ribonucleoside (MPR). This elaborately designed cluster, Au5(MPR)2, can form a stable intramolecular CT state after light excitation, and exhibits long-lived color-tunable phosphorescence. After the cleavage by purine nucleoside phosphorylase (PNP), the CT triplet state can be easily directed to a low-lying energy level, leading to a bathochromic shift of the emission band accompanied by weaker and shorter-lived luminescence. Remarkably, these ligand-engineered AuNCs show high affinity towards PNP as well as decent performance for analyzing and visualizing enzyme activity and related drugs. The work of this paper provides a good example for diversifying physicochemical properties and application scenarios of MNCs by rational ligand engineering, which will facilitate future interest and new strategies to precisely engineer solution-based nanocluster materials.

Planar Core and Macrocyclic Shell Stabilized Atomically Precise Copper Nanocluster Catalyst for Efficient Hydroboration of C-C Multiple Bond

Atomically precise metal nanoclusters (NCs) have become an important class of catalysts due to their catalytic activity, high surface area, and tailored active sites. However, the design and development of bond-forming reaction catalysts based on copper NCs are still in their early stages. Herein, we report the synthesis of an atomically precise copper nanocluster with a planar core and unique shell, [Cu45(TBBT)29(TPP)4(C4H11N)2H14]2+ (Cu45) (TBBT: 4-tert-butylbenzenethiol; TPP: triphenylphosphine), in high yield via a one-pot reduction method. The resulting structurally well-defined Cu45 is a highly efficient catalyst for the hydroboration reaction of alkynes and alkenes. Mechanistic studies show that a single-electron oxidation of the in situ-formed ate complex enables the hydroboration via the formation of boryl-centered radicals under mild conditions. This work demonstrates the promise of tailored copper nanoclusters as catalysts for C-B heteroatom bond-forming reactions. The catalysts are compatible with a wide range of alkynes and alkenes and functional groups for producing hydroborated products.

Platinum-Grafted Twenty-Five Atom Gold Nanoclusters for Robust Hydrogen Evolution

A robust hydrogen evolution is demonstrated from Au25(PET)18]- nanoclusters (PET = 2-phenylethanethiol) grafted with minimal platinum atoms. The fabrication involves an electrochemical activation of nanoclusters by partial removal of thiols, without affecting the metallic core, which exposes Au-sites adsorbed with hydrogen and enables an electroless grafting of platinum. The exposed Au-sites feature the (111)-facet of the fcc-Au25 nanoclusters as assessed through lead underpotential deposition. The electrochemically activated nanoclusters (without Pt loading) show better electrocatalytic reactivity toward hydrogen evolution reaction than the pristine nanoclusters in an acidic medium. The platinum-grafted nanocluster outperformed with a lower overpotential of 0.117 V vs RHE (RHE = Reversible Hydrogen Electrode) compared to electrochemically activated nanoclusters (0.353 V vs RHE ) at 10 mA cm-2 and is comparable with commercial Pt/C. The electrochemically activated nanoclusters show better reactivity at higher current density owing to the ease of hydrogen release from the active sites. The modified nanoclusters show unique supramolecular self-assembly characteristics as observed in electron microscopy and tomography due to the possible metallophilic interactions. These results suggest that the post-surface modification of nanoclusters will be an ideal tool to address the sustainable production of green hydrogen.

Ag1+ incorporation via a Zr4+-anchored metalloligand: fine-tuning catalytic Ag sites in Zr/Ag bimetallic clusters for enhanced eCO2RR-to-CO activity

Attaining meticulous dominion over the binding milieu of catalytic metal sites remains an indispensable pursuit to tailor product selectivity and elevate catalytic activity. By harnessing the distinctive attributes of a Zr4+-anchored thiacalix[4]arene (TC4A) metalloligand, we have pioneered a methodology for incorporating catalytic Ag1+ sites, resulting in the first Zr-Ag bimetallic cluster, Zr2Ag7, which unveils a dualistic configuration embodying twin {ZrAg3(TC4A)2} substructures linked by an {AgSal} moiety. This cluster unveils a trinity of discrete Ag sites: a pair ensconced within {ZrAg3(TC4A)2} subunits and one located between two units. Expanding the purview, we have also crafted ZrAg3 and Zr2Ag2 clusters, meticulously mimicking the two Ag site environment inherent in the {ZrAg3(TC4A)2} monomer. The distinct structural profiles of Zr2Ag7, ZrAg3, and Zr2Ag provide an exquisite foundation for a precise comparative appraisal of catalytic prowess across three Ag sites intrinsic to Zr2Ag7. Remarkably, Zr2Ag7 eclipses its counterparts in the electroreduction of CO2, culminating in a CO faradaic efficiency (FECO) of 90.23% at -0.9 V. This achievement markedly surpasses the performance metrics of ZrAg3 (FECO: 55.45% at -1.0 V) and Zr2Ag2 (FECO: 13.09% at -1.0 V). Utilizing in situ ATR-FTIR, we can observe reaction intermediates on the Ag sites. To unveil underlying mechanisms, we employ density functional theory (DFT) calculations to determine changes in free energy accompanying each elementary step throughout the conversion of CO2 to CO. Our findings reveal the exceptional proficiency of the bridged-Ag site that interconnects paired {ZrAg3(TC4A)2} units, skillfully stabilizing *COOH intermediates, surpassing the stabilization efficacy of the other Ag sites located elsewhere. The invaluable insights gleaned from this pioneering endeavor lay a novel course for the design of exceptionally efficient catalysts tailored for CO2 reduction reactions, emphatically underscoring novel vistas this research unshrouds.

Stepwise structural evolution toward robust carboranealkynyl-protected copper nanocluster catalysts for nitrate electroreduction

Atomically precise metal nanoclusters (NCs) are emerging as idealized model catalysts for imprecise metal nanoparticles to unveil their structure-activity relationship. However, the directional synthesis of robust metal NCs with accessible catalytic active sites remains a great challenge. In this work, we achieved bulky carboranealkynyl-protected copper NCs, the monomer Cu13·3PF6 and nido-carboranealkynyl bridged dimer Cu26·4PF6, with fair stability as well as accessible open metal sites step by step through external ligand shell modification and metal-core evolution. Both Cu13·3PF6 and Cu26·4PF6 demonstrate remarkable catalytic activity and selectivity in electrocatalytic nitrate (NO3-) reduction to NH3 reaction, with the dimer Cu26·4PF6 displaying superior performance. The mechanism of this catalytic reaction was elucidated through theoretical computations in conjunction with in situ FTIR spectra. This study not only provides strategies for accessing desired copper NC catalysts but also establishes a platform to uncover the structure-activity relationship of copper NCs.

Enzyme-Inspired Ligand Engineering of Gold Nanoclusters for Electrocatalytic Microenvironment Manipulation

Natural enzymes intricately regulate substrate accessibility through specific amino acid sequences and folded structures at their active sites. Achieving such precise control over the microenvironment has proven to be challenging in nanocatalysis, especially in the realm of ligand-stabilized metal nanoparticles. Here, we use atomically precise metal nanoclusters (NCs) as model catalysts to demonstrate an effective ligand engineering strategy to control the local concentration of CO2 on the surface of gold (Au) NCs during electrocatalytic CO2 reduction reactions (CO2RR). The precise incorporation of two 2-thiouracil-5-carboxylic acid (TCA) ligands within the pocket-like cavity of [Au25(pMBA)18]- NCs (pMBA = para-mercaptobenzoic acid) leads to a substantial acceleration in the reaction kinetics of CO2RR. This enhancement is attributed to a more favorable microenvironment in proximity to the active site for CO2, facilitated by supramolecular interactions between the nucleophilic Nδ- of the pyrimidine ring of the TCA ligand and the electrophilic Cδ+ of CO2. A comprehensive investigation employing absorption spectroscopy, mass spectrometry, isotopic labeling measurements, electrochemical analyses, and quantum chemical computation highlights the pivotal role of local CO2 enrichment in enhancing the activity and selectivity of TCA-modified Au25 NCs for CO2RR. Notably, a high Faradaic efficiency of 98.6% toward CO has been achieved. The surface engineering approach and catalytic fundamentals elucidated in this study provide a systematic foundation for the molecular-level design of metal-based electrocatalysts.

Ligand-controlled exposure of active sites on the Pd1Ag14 nanocluster surface to boost electrocatalytic CO2 reduction

Advancing catalyst design requires meticulous control of nanocatalyst selectivity at the atomic level. Here, we synthesized two Pd1Ag14 nanoclusters: Pd1Ag14(PPh3)8(SPh(CF3)2)6 and Pd1Ag14(P(Ph-p-OMe)3)7(SPh)6, each with well-defined structures. Notably, in Pd1Ag14(P(Ph-p-OMe)3)7(SPh)6, the detachment of a phosphine ligand from the top silver atom facilitates the exposure of singular active sites. This exposure significantly enhances its selectivity for the electrocatalytic reduction of CO2 to CO, achieving a Faraday efficiency of 83.3% at -1.3 V, markedly surpassing the 28.1% performance at -1.2 V of Pd1Ag14(PPh3)8(SPh(CF3)2)6. This work underscores the impact of atomic-level structural manipulation on enhancing nanocatalyst performance.

Synthesis and cluster structure distortions of biscarborane dithiol, thioether, and disulfide

The synthesis and structural characterization of the first sulfur-containing derivatives of the C,C-biscarborane {ortho-C2B10}2 cluster - thiol, thioether, and disulfide - are reported. The biscarboranyl dithiol (1-HS-C2B10H10)2 exhibits an exceedingly long intracluster carbon-carbon bond length of 1.858(3) Å, which is attributed to the extensive interaction between the lone pairs of the thiol groups and the unoccupied molecular orbital of the carborane cluster. The structures of the doubly deprotonated biscarboranyl dithiolate anion (1-S-C2B10H10)22- with various counter cations feature an even longer carbon-carbon bond length of 2.062(10) Å within the cluster along with a short carbon-sulfur bond of 1.660(7) Å, both indicative of significant delocalization of electron density from the sulfur atoms into the cluster.

Tailoring the subshell and electronic structure of an atomically precise AuAg alloy nanocluster

Manipulating the atomic-level structure of the subshell of a nanocluster while preserving the inner and outer shell structure is challenging. We present the synthesis and molecular structure of an alkynyl-protected Au34Ag27 nanocluster, which exhibits distinct third shell atomic arrangement, electronic structure, and optical properties from those of the Au34Ag28 nanocluster.

Symmetry Breaking Enhancing the Activity of Electrocatalytic CO2 Reduction on an Icosahedron-Kernel Cluster by Cu Atoms Regulation

Recently, CO2 hydrogenation had a new breakthrough resulting from the design of catalysts to effectively activate linear CO2 with symmetry-breaking sites. However, understanding the relationship between symmetry-breaking sites and catalytic activity at the atomic level is still a great challenge. In this study, a set of gold-copper alloy Au13 Cux (x=0-4) nanoclusters were used as research objects to show the symmetry-controlled breaking structure on the surface of nanoclusters with the help of manipulability of the Cu atoms. Among them, Au13 Cu3 nanocluster displays the highest degree of symmetry-breaking on its crystal structure compared with the other nanoclusters in the family. Where the three copper atoms occupying the surface of the icosahedral kernel unevenly with one copper atom is coordinately unsaturated (CuS2 motif relative to CuS3 motif). As expected, Au13 Cu3 has an excellent hydrogenation activity of CO2 , in which the current density is as high as 70 mA cm-2 (-0.97 V) and the maximum FECO reaches 99 % at -0.58 V. Through the combination of crystal structures and theoretical calculations, the excellent catalytic activity of Au13 Cu3 is revealed to be indeed closely related to its asymmetric structure.

Nanocluster Surface Microenvironment Modulates Electrocatalytic CO2 Reduction

The catalytic activity and product selectivity of the electrochemical CO2 reduction reaction (eCO2 RR) depend strongly on the local microenvironment of mass diffusion at the nanostructured catalyst and electrolyte interface. Achieving a molecular-level understanding of the electrocatalytic reaction requires the development of tunable metal-ligand interfacial structures with atomic precision, which is highly challenging. Here, the synthesis and molecular structure of a 25-atom silver nanocluster interfaced with an organic shell comprising 18 thiolate ligands are presented. The locally induced hydrophobicity by bulky alkyl functionality near the surface of the Ag25 cluster dramatically enhances the eCO2 RR activity (CO Faradaic efficiency, FECO : 90.3%) with higher CO partial current density (jCO ) in an H-cell compared to Ag25 cluster (FECO : 66.6%) with confined hydrophilicity, which modulates surface interactions with water and CO2 . Remarkably, the hydrophobic Ag25 cluster exhibits jCO as high as -240 mA cm-2 with FECO >90% at -3.4 V cell potential in a gas-fed membrane electrode assembly device. Furthermore, this cluster demonstrates stable eCO2 RR over 120 h. Operando surface-enhanced infrared absorption spectroscopy and theoretical simulations reveal how the ligands alter the neighboring water structure and *CO intermediates, impacting the intrinsic eCO2 RR activity, which provides atomistic mechanistic insights into the crucial role of confined hydrophobicity.

Copper-Sulfur-Nitrogen Cluster Providing a Local Proton for Efficient Carbon Dioxide Photoreduction

Atomically precise Cu clusters are highly desirable as catalysts for CO2 reduction reaction (CO2 RR), and they provide an appropriate model platform for elaborating their structure-activity relationship. However, an efficient overall photocatalytic CO2 RR with H2 O using assembled Cu-cluster aggregates as single component photocatalyst has not been reported. Herein, we report a stable crystalline Cu-S-N cluster photocatalyst with local protonated N-H groups (denoted as Cu6 -NH). The catalyst exhibits suitable photocatalytic redox potentials, high structural stability, active catalytic species, and a narrow band gap, which account for its outstanding photocatalytic CO2 RR performance under visible light, with ≈100 % selectivity for CO evolution. Remarkably, systematic isostructural Cu-cluster control experiments, in situ infrared spectroscopy, and density functional theory calculations revealed that the protonated pyrimidine N atoms in the Cu6 -NH cluster act as a proton relay station, providing a local proton during the photocatalytic CO2 RR. This efficiently lowers the energy barrier for the formation of the *COOH intermediate, which is the rate-limiting step, efficiently enhancing the photocatalytic performance. This work lays the foundation for the development of atomically precise metal-cluster-based photocatalysts.

PtAg18 superatoms costabilized by phosphines and halides: synthesis, structure, and catalysis

Reported herein is the facial synthesis, molecular structure, and catalysis of a Pt/Ag nanocluster costabilized by organic ligands of phosphines and inorganic ligands of chlorides. The nanocluster with molecular formula of [PtAg18(dppp)6Cl8](SbF6)2 has been obtained facilely by the one pot method. The structure of the cluster could be anatomized as the stabilizaiton of PtAg12-centered icosahedral core by the metalloligand of dppp-Ag-Cl, in which Cl- not only caps the surface Ag atoms but also binds the core and surface motifs. Featuring eight free electrons in its structure, the cluster exhibits high stability. More interestingly, the exposure of surface metal sites endows the cluster with counterintutively  high catalytic activity in hydrogenation reactions.

One-step preparation of Pt/Ag nanoclusters for CO2 transformation

Structurally precise metal nanoclusters with a facile synthetic process and high catalytic performance have been long pursued. These atomically precise nanocatalysts are regarded as model systems to study structure-performance relationships, surface coordination chemistry, and the reaction mechanism of heterogeneous metal catalysts. Nevertheless, the research on silver-based nanoclusters for driving chemical transformations is sluggish in comparison to gold counterparts. Herein, we report the one-step synthesis of Pt/Ag alloy nanoclusters of [PtAg9(C18H12Br3P)7Cl3](C18H12Br3P), which are highly active in catalysing cycloaddition reactions of CO2 and epoxides. The cluster was obtained in a rather simple way with the reduction of silver and platinum salts in the presence of ligands in one pot. The molecular structure of the titled cluster describes the protection of the Pt-centred Ag9 crown by the shell of phosphine ligands and halides. Its electronic structure, as revealed by density function theoretical calculations, adopts a superatomic geometry with 1S21P6 configuration. Interestingly, the cluster displays high activity in the formation of cyclic carbonates from CO2 under mind conditions.

Template-assisted synthesis of isomeric copper(i) clusters with tunable structures showing photophysical and electrochemical properties

A comparative study of structure-property relationships in isomeric and isostructural atomically precise clusters is an ideal approach to unravel their fundamental properties. Herein, seven high-nuclearity copper(i) alkynyl clusters utilizing template-assisted strategies were synthesized. Spherical Cu36 and Cu56 clusters are formed with a [M@(V/PO4)6] (M: Cu2+, Na+, K+) skeleton motif, while peanut-shaped Cu56 clusters feature four separate PO4 templates. Experiments and theoretical calculations suggested that the photophysical properties of these clusters are dependent on both the inner templates and outer phosphonate ligands. Phenyl and 1-naphthyl phosphate-protected clusters exhibited enhanced emission features attributed to numerous well-arranged intermolecular C-H⋯π interactions between the ligands. Moreover, the electrocatalytic CO2 reduction properties suggested that internal PO4 templates and external naphthyl groups could promote an increase in C2 products (C2H4 and C2H5OH). Our research provides new insight into the design and synthesis of multifunctional copper(i) clusters, and highlights the significance of atomic-level comparative studies of structure-property relationships.

Hydride-doped Ag17Cu10 nanoclusters as high-performance electrocatalysts for CO2 reduction

The atomically precise metal electrocatalysts for driving CO2 reduction reactions are eagerly pursued as they are model systems to identify the active sites, understand the reaction mechanism, and further guide the exploration of efficient and practical metal nanocatalysts. Reported herein is a nanocluster-based electrocatalyst for CO2 reduction, which features a clear geometric and electronic structure, and more importantly excellent performance. The nanocatalysts with the molecular formula of [Ag17Cu10(dppm)4(PhC≡C)20H4]3+ have been obtained in a facile way. The unique metal framework of the cluster, with silver, copper, and hydride included, and dedicated surface structure, with strong (dppm) and labile (alkynyl) ligands coordinated, endow the cluster with excellent performance in electrochemical CO2 reduction reaction to CO. With the atomically precise electrocatalysts in hand, not only high reactivity and selectivity (Faradaic efficiency for CO up to 91.6%) but also long-term stability (24 h), are achieved.

Stepwise assembly of thiacalix[4]arene-protected Ag/Ti bimetallic nanoclusters: accurate identification of catalytic Ag sites in CO2 electroreduction

The accurate identification of catalytic sites in heterogeneous catalysts poses a significant challenge due to the intricate nature of controlling interfacial chemistry at the molecular level. In this study, we introduce a novel strategy to address this issue by utilizing a thiacalix[4]arene (TC4A)-protected Ti-oxo core as a template for loading Ag1+ ions, leading to the successful synthesis of a unique Ag/Ti bimetallic nanocluster denoted as Ti8Ag8. This nanocluster exhibits multiple surface-exposed Ag sites and possesses a distinctive "core-shell" structure, consisting of a {Ti4@Ag8(TC4A)4} core housing a {Ti2O2@Ag4(TC4A)2} motif and two {Ti@Ag2(TC4A)} motifs. To enable a comprehensive analysis, we also prepared a Ti2Ag4 cluster with the same {Ti2O2@Ag4(TC4A)2} structure found within Ti8Ag8. The structural disparities between Ti8Ag8 and Ti2Ag4 provide an excellent platform for a comparison of catalytic activity at different Ag sites. Remarkably, Ti8Ag8 exhibits exceptional performance in the electroreduction of CO2 (eCO2RR), showcasing a CO faradaic efficiency (FECO) of 92.33% at -0.9 V vs. RHE, surpassing the FECO of Ti2Ag4 (69.87% at -0.9 V vs. RHE) by a significant margin. Through density functional theory (DFT) calculations, we unveil the catalytic mechanism and further discover that Ag active sites located at {Ti@Ag2(TC4A)} possess a higher εd value compared to those at {Ti2O2@Ag4(TC4A)2}, enhancing the stabilization of the *COOH intermediate during the eCO2RR. This study provides valuable insights into the accurate identification of catalytic sites in bimetallic nanoclusters and opens up promising avenues for efficient CO2 reduction catalyst design.

Recent Advances in Ligand Engineering for Gold Nanocluster Catalysis: Ligand Library, Ligand Effects and Strategies

Advances in new ligands in the last decade facilitated in-depth studies on the property-relationship of gold nanoclusters and promoted the rational synthesis and related applications of such materials. Currently, more and more new ligands are being explored; thus, the ligand library of AuNCs is being expanded fast, which also enables investigation of ligand effects of AuNCs via direct comparison of different ligating shell with the identical gold core. It is now widely accepted that ligands influence the properties of AuNCs enormously including stability, catalysis, photoluminescence among others. These studies inspired ligand engineering of AuNCs. One of the goals for ligand engineering is to develop ligated AuNC catalysts in which the ligands are able to exert big-enough influence on electronic and steric control over catalysis as in a transition-metal or an enzyme system. Although increasing attention is paid to the further expansion of ligand library, the investigation of design principles and strategies regarding ligands are still in their infant stage. This review summarizes the ligands for AuNC synthesis, the ligand effects on stability and catalysis, and recently developed strategies in promoting AuNC catalytic performance via ligand manipulation.

Unveiling the Remarkable Stability and Catalytic Activity of a 6-Electron Superatomic Ag30 Nanocluster for CO2 Electroreduction

Nanocluster catalysts face a significant challenge in striking the right balance between stability and catalytic activity. Here, we present a thiacalix[4]arene-protected 6-electron [Ag30(TC4A)4(iPrS)8] nanocluster that demonstrates both high stability and catalytic activity. The Ag30 nanocluster features a metallic core, Ag104+, consisting of two Ag3 triangles and one Ag4 square, shielded by four {Ag5@(TC4A)4} staple motifs. Based on DFT calculations, the Ag104+ metallic kernel can be viewed as a trimer comprising 2-electron superatomic units, exhibiting a valence electron structure similar to that of the Be3 molecule. Notably, this is the first crystallographic evidence of the trimerization of 2-electron superatomic units. Ag30 can reduce CO2 into CO with a Faraday efficiency of 93.4% at -0.9 V versus RHE along with excellent long-term stability. Its catalytic activity is far superior to that of the chain-like AgI polymer ∞1{[H2Ag5(TC4A)(iPrS)3]} (∞1Agn), with the composition similar to Ag30. DFT calculations elucidated the catalytic mechanism to clarify the contrasting catalytic performances of the Ag30 and ∞1Agn polymers and disclosed that the intrinsically higher activity of Ag30 may be due to the greater stability of the dual adsorption mode of the *COOH intermediate on the metallic core.

Atomically Precise Copper Nanoclusters for Highly Efficient Electroreduction of CO2 towards Hydrocarbons via Breaking the Coordination Symmetry of Cu Site

We propose an effective highest occupied d-orbital modulation strategy engendered by breaking the coordination symmetry of sites in the atomically precise Cu nanocluster (NC) to switch the product of CO2 electroreduction from HCOOH/CO to higher-valued hydrocarbons. An atomically well-defined Cu6 NC with symmetry-broken Cu-S2 N1 active sites (named Cu6 (MBD)6 , MBD=2-mercaptobenzimidazole) was designed and synthesized by a judicious choice of ligand containing both S and N coordination atoms. Different from the previously reported high HCOOH selectivity of Cu NCs with Cu-S3 sites, the Cu6 (MBD)6 with Cu-S2 N1 coordination structure shows a high Faradaic efficiency toward hydrocarbons of 65.5 % at -1.4 V versus the reversible hydrogen electrode (including 42.5 % CH4 and 23 % C2 H4 ), with the hydrocarbons partial current density of -183.4 mA cm-2 . Theoretical calculations reveal that the symmetry-broken Cu-S2 N1 sites can rearrange the Cu 3d orbitals withd x 2 - y 2 ${d_{x^2 - y^2 } }$ as the highest occupied d-orbital, thus favoring the generation of key intermediate *COOH instead of *OCHO to favor *CO formation, followed by hydrogenation and/or C-C coupling to produce hydrocarbons. This is the first attempt to regulate the coordination mode of Cu atom in Cu NCs for hydrocarbons generation, and provides new inspiration for designing atomically precise NCs for efficient CO2 RR towards highly-valued products.

Programmable kernel structures of atomically precise metal nanoclusters for tailoring catalytic properties

The unclear structures and polydispersity of metal nanoparticles (NPs) seriously hamper the identification of the active sites and the construction of structure-reactivity relationships. Fortunately, ligand-protected metal nanoclusters (NCs) with atomically precise structures and monodispersity have become an ideal candidate for understanding the well-defined correlations between structure and catalytic property at an atomic level. The programmable kernel structures of atomically precise metal NCs provide a fantastic chance to modulate their size, shape, atomic arrangement, and electron state by the precise modulating of the number, type, and location of metal atoms. Thus, the special focus of this review highlights the most recent process in tailoring the catalytic activity and selectivity over metal NCs by precisely controlling their kernel structures. This review is expected to shed light on the in-depth understanding of metal NCs' kernel structures and reactivity relationships.

Ultrasmall Coinage Metal Nanoclusters as Promising Theranostic Probes for Biomedical Applications

Ultrasmall coinage metal nanoclusters (NCs, <3 nm) have emerged as a novel class of theranostic probes due to their atomically precise size and engineered physicochemical properties. The rapid advances in the design and applications of metal NC-based theranostic probes are made possible by the atomic-level engineering of metal NCs. This Perspective article examines (i) how the functions of metal NCs are engineered for theranostic applications, (ii) how a metal NC-based theranostic probe is designed and how its physicochemical properties affect the theranostic performance, and (iii) how metal NCs are used to diagnose and treat various diseases. We first summarize the tailored properties of metal NCs for theranostic applications in terms of biocompatibility and tumor targeting. We focus our discussion on the theranostic applications of metal NCs in bioimaging-directed disease diagnosis, photoinduced disease therapy, nanomedicine, drug delivery, and optical urinalysis. Lastly, an outlook on the challenges and opportunities in the future development of metal NCs for theranostic applications is provided.

Cocrystallization of Two Negatively Charged Dimercaptomaleonitrile-Stabilized Silver Nanoclusters

Studies on the assembly of atomically precise metal nanoclusters (NCs) are of great significance in the nanomaterial field, which has attracted increasing interest in the last few decades. Herein, we report the cocrystallization of two negatively charged atom-precise silver nanoclusters, the octahedral [Ag₆₂(MNT)₂₄(TPP)₆]^8- (Ag₆₂) and the truncated-tetrahedral [Ag₂₂(MNT)₁₂(TPP)₄]^4- (Ag₂₂) in a 1:2 ratio (MNT^2- = dimercaptomaleonitrile, TPP = triphenylphosphine). As far as we know, a cocrystal containing two negatively charged NCs has seldom been reported. Single-crystal structure determinations reveal that the component Ag₂₂ and Ag₆₂ NCs both adopt core-shell structures. In addition, the component NCs were separately obtained by adjusting the synthetic conditions. This work enriches the structural diversity of silver NCs and extends the family of cluster-based cocrystals.

Body-Centered-Cubic-Kernelled Ag15Cu6 Nanocluster with Alkynyl Protection: Synthesis, Total Structure, and CO2 Electroreduction

While atomically monodisperse nanostructured materials are highly desirable to unravel the size- and structure-catalysis relationships, their controlled synthesis and the atomic-level structure determination pose challenges. Particularly, copper-containing atomically precise alloy nanoclusters are potential catalyst candidates for the electrochemical CO₂ reduction reaction (eCO₂RR) due to high abundance and tunable catalytic activity of copper. Herein, we report the synthesis and total structure of an alkynyl-protected 21-atom AgCu alloy nanocluster [Ag₁₅Cu₆(C≡CR)₁₈(DPPE)₂]^-, denoted as Ag₁₅Cu₆ (HC≡CR: 3,5-bis(trifluoromethyl)phenylacetylene; DPPE: 1,2-bis(diphenylphosphino)ethane). The single-crystal X-ray diffraction reveals that Ag₁₅Cu₆ consists of an Ag₁₁Cu₄ metal core exhibiting a body-centered cubic (bcc) structure, which is capped by 2 Cu atoms, 2 Ag₂DPPE motifs, and 18 alkynyl ligands. Interestingly, the Ag₁₅Cu₆ cluster exhibits excellent catalytic activity for eCO₂RR with a CO faradaic efficiency (FE_CO) of 91.3% at -0.81 V (vs the reversible hydrogen electrode, RHE), which is much higher than that (FE_CO: 48.5% at -0.89 V vs RHE) of Ag₉Cu₆ with bcc structure. Furthermore, Ag₁₅Cu₆ shows superior stability with no significant decay in the current density and FE_CO during a long-term operation of 145 h. Density functional theory calculations reveal that the de-ligated Ag₁₅Cu₆ cluster can expose more space at the pair of AgCu dual metals as the efficient active sites for CO formation.

Structural Engineering toward Gold Nanocluster Catalysis

Atomically precise gold nanoclusters provide great opportunities to explore the relationship between the structure and properties of nanogold catalysts. A nanocluster consists of a metal core and a surface ligand shell, and both the core and shell have significant effects on the catalytic properties. Thanks to their precise structures, the active metal site of the clusters can be readily identified and the effects of ligands on catalysis can be disclosed. In this Minireview, we summarize recent advances in catalytic research of gold nanoclusters, emphasizing four strategies for constructing open metal sites, including by post-treatment, the bulky ligands strategy, the surface geometric mismatch method, and heteroatom doping procedures. We also discuss the effects of ligands on the catalytic activity, selectivity, and stability of gold cluster catalysts. Finally, we present future challenges relating to gold cluster catalysis.

Electrocatalytic CO2 Reduction over Atomically Precise Metal Nanoclusters Protected by Organic Ligands

The electrochemical carbon dioxide reduction reaction (CO₂RR) is a promising method to realize carbon recycling and sustainable development because of its mild reaction conditions and capability to utilize the electric power generated by renewable energy such as solar, wind, or tidal energy to produce high-value-added liquid fuels and chemicals. However, it is still a great challenge to deeply understand the reaction mechanism of CO₂RRs involving multiple chemical processes and multiple products due to the complexity of the traditional catalyst's surface. Organic ligand-protected metal nanoclusters (NCs) with accurate compositions and definite atom packing structures show advantages for revealing the reaction mechanism of CO₂RRs. This Review focuses on the recent progress in CO₂RRs catalyzed by atomically precise metal NCs, including gold, copper, and silver NCs. Particularly, the influences of charge, ligand, surface structure, doping of Au NCs, and binders on the CO₂RR are discussed in detail. Meanwhile the reaction mechanisms of CO₂RRs including the active sites and the key reaction intermediates are also discussed. It is expected that progress in this research area could promote the development of metal NCs and CO₂RRs.